In the process for the recovery of zinc from minerals, mineral concentrates may be treated in a variety of ways that include the roast-leach-electrowinning and the pressure leach-electrowinning processes. During processing, many zinc-containing sulfate solutions are encountered from which it is often desirable to recover both the zinc and the sulfuric acid. Such solutions may contain from relatively low to relatively high amounts of zinc, sulfuric acid or both. For example, in the electrowinning of zinc from zinc sulfate electrolyte, purified electrolyte is subjected to electrolysis, zinc is deposited on the cathodes and recovered, and a portion of the circulating electrolyte is purged as spent acid to control the accumulation of impurities. Other solutions encountered in hydrometallurgical zinc processes, for example, are ones that contain zinc, sulfuric acid and other metal values and impurities. Such solutions are often treated first for the recovery of metal values and the residual solutions must then be treated before discarding to prevent ecological damage. Similarly, solutions containing small amounts of zinc and concentrations of certain impurities must be treated prior to discharge to the environment.